The overall objectives of this proposed research will be to elucidate on a biochemical level the specificity, affinity and the nature of the binding of the major species of oral streptococci (Streptococcus sanguis, Streptococcus mutans, Streptococcus mitis) and oral haemophili (primarily Haemophilus parainfluenzae) to each other and to the tooth surface. Isolation and partial purification of bacterial cell surface ligands which promote attachment to the tooth or other bacteria will facilitate these objectives. These studies will also be extended to better understand the ecological relationships between bacterial adherence to the tooth and to other bacteria, as these phenomena relate to the colonization and particularly accumulation of dental plaque on the tooth surface. Both in vivo and in vitro adherence and colonization studies will be conducted to provide additional insight into supragingival dental plaque microbial ecology. The specific aims of this proposed research will be to: 1) further purify the cell surface adhesins from Haemophilus spp., particularly H. parainfluenzae, and characterize them biochemically; 2) examine comparatively the adhesins from the streptococci and haemophili in in vitro assays as to their functional relatedness in adherence to saliva-coated phydroxyapatite (SHA) and to each other; 3) study the in vivo colonization of the major species of streptococci, haemophili, Actinomyces, Fusobacterium, Capnocytophaga and Bacteroides species to the teeth as developing supragingival dental plaque; 4) determine the role of interbacterial adherence in colonization of the tooth surface in vivo, and vitro to SHA. These studies will lead to a better understanding of the important ecological role of the persistent and numerically predominant species in developing plaque, S. sanguis, which is both noncariogenic and nonperiodontopathic. Greater understanding of the species found in vivo in developing plaque can logically lead to better preventive measures in the control of dental diseases, as well as provide specific parameters for the accurate prediction of individual dental disease risks, and aid the ability to accurately assess the efficacy of preventive measures and various treatment regimes.